• Journal of Energy Engineering
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• v.13 no.1
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• pp.51-59
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• 2004

The NSSS (Nuclear Steam Supply System) thermal-hydraulic programs adopted in the domestic full-scope power plant simulators were provided in early 1980s by foreign vendors. Because of limited compulsational capability at that time, they usually used very simplified physical models for a real-time simulation of NSSS thermal-hydraulic transients, which entails inaccurate results and, thus, the possibility of so-called "negative training", especially for complicated two-phase flows in the reactor coolant system. In resolve the problem, KEPRI developed a realistic NSSS T/H program ARTS which was based on the RETRAN-3D code for the improvement of the Nuclear Power Plant full-scope simulator. The ARTS (based on the RETRAN-3D code) guarantees the real-time calculations of almost all transients and ensures the robustness of simulations. However, there is some possibility of failing to calculate in the case of large break loss of coolant accident (LBLOCA) and low-pressure low-flow transient. In this case, the backup calculation system cover automatically the ARTS. The backup calculation system was expected to provide substantially more accurate predictions in the analysis of the system transients involving LBLOCA. The results were reasonable in terms of accuracy, real-time simulation, robustness and education of operators, complying with FSAR and the AMSI/ANS-3.5-1998 simulator software performance criteria.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.439-449
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• 2019

To prevent the drying-out of streams and to make effective use of stream water and groundwater, it is necessary to evaluate the impact of groundwater pumping on nearby streams. To this end, stream depletion due to groundwater pumping should be investigated in terms of various hydraulic characteristics of the aquifer and stream. This study used the Baalousha analytical solution, which accounts for stream-stage variation over time, to analyze stream depletion due to groundwater pumping for cases where the stream level decreases exponentially and recovers after the decrease. For conditions such as an aquifer transmissivity of 10~100 ㎡ d^-1, storage coefficient 0.05~0.3, streambed hydraulic conductance 0.1~1.0 m d^-1, stream-well distance 100~500 m, and stage recession coefficient 0.1~1.0 d^-1, the contribution of stream water (the dimensionless ratio of stream water reduction rate to groundwater pumping rate) was analyzed in cases where stream level change was considered. Considering the effect of stream-stage recession, the contribution of stream water is greatly reduced and is less affected by the stream-depletion factor, which is a function of the stream-to-well distance and hydraulic diffusivity. However, there is no significant difference in stream depletion under constant- and variable-stage recovery after recession. These results indicate that stream level control can distribute the relative impacts on stream water and aquifer storage during groundwater pumping

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.1
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• pp.38-49
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• 2015

Past study of tsunami heavily relied on the numerical modelling using 2D Boussinesq Eq. and Solitary wave. Lately, based on the fact that numerically simulated run up heights based on solitary wave are somewhat smaller than the measured one, Leading Depression N (LDN) Wave has been elaborated, which can account the advancement of a shore line before tsunami strikes a shore. Thereafter it is reported that more accurate simulation can be possible once LDN is deployed. On the other hand, there were numerous reports indicating that stable LDN wave can't be sustained in the hydraulic model test. These conflicts between the hydraulic model tests and numerical results have their roots on the assumption made in the derivation of Boussinesq type wave model such as that wave nonlinearity is equally balanced with wave dispersiveness. Hence, in the numerical simulation based on the Boussinesq type wave model, wave dispersiveness is inevitably underestimated, especially in deep water. Based on this rationale, we developed the modified methodology for the generation of stable LDN wave in the 3D numerical wave flume, and proceeded to numerically analyze the depression effect of Hybrid Breaker on the run up height due to tsunami using the Navier Stoke Equation. The verification of newly proposed wave model in this study was carried out using the run up height from the hydraulic model test. It was shown that Hybrid Breaker consisting of three water chamber and slope at its front can reduce 13% of run up height for H = 5m, and 10% of run up height for H = 6m.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.28-35
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• 2017

Recently, conventional hydraulic car lift systems face the technological limitations due to a lack of height control. The demand for height controllability is required in many tasks such as wheel alignment, and requires compensation for the structural deformation of the lift caused by irregular load distribution. In order to resolve this limitation of the conventional car lift, in this work, a new type of a hydraulic vehicle lift using a magneto-rheological (MR) valve system is proposed and analyzed. Firstly, the dynamic model of vehicle lift is formulated to evaluate control performance; subsequently, an MR valve is designed to obtain the desired pressure drop required in the car lift. Next, a proportional-integral-derivative (PID) controller is formulated to achieve accurate control of the lifting height and then computer simulations are undertaken to show accurate height control performances of the proposed new car lift system.

• Journal of Drive and Control
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• v.14 no.1
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• pp.14-22
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• 2017

Flow force is the additional unbalanced force acting on the valve spool by fluid flow, excluding the static pressure force that is offset on the spool land wall at the same magnitude. When designing the valve spool, it is assumed that the same average value of static pressure is applied to the inlet and outlet spool land wall in one chamber. However, the high velocity of the fluid flow by the inlet or outlet metering orifice creates unbalanced pressure distribution and generates additional force in the opposite direction to that of the solenoid attraction force. This flow force has a negative effect on the control performance of the EPPR valve, which needs to develop uniform output pressure along the entire spool control range. In this study, we developed a 3D model of the EPPR valve and conducted flow force characteristic analysis using CFD S/W (ANSYS FLUENT). The alleviated flow force model was derived by adjusting the design parameters of the spool notch.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.1
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• pp.72-82
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• 2015

In order to effectively and economically apply the previous POM(Princeton Ocean Model) WAD(Wetting And Drying) to the coastal area, the POM WAD was modified such as the water elevation input of tidal harmonics in the open boundaries was included and a CTS(Computing Time Saving) technique was introduced to the model. The modified model was tested to the standing waves in the rectangular bay and the hydraulic experiments for the flow and heat diffusion in the 3D basin. The numerical results showed a good agreement with the analytical solutions of the standing waves and the observed values by the hydraulic experiments, respectively. And also when the modified model with the CTS technique was applied to Gwangyang Bay of Korea, the computing time was decreased by as much as 39.4%.

• Ecology and Resilient Infrastructure
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• v.1 no.1
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• pp.8-18
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• 2014

This study analyzes characteristics of flow using 3 dimensional numerical model, Delft3D, at the downstream of hydraulic structure. And fish shelters are suggested by analyzing them in flood time. A hydraulic structure changes flow conveyance, water depth and velocity affecting the activity of the fish. Flow depth decreases and velocity is fast near the left bank at the downstream of Gumi weir because of the concentration of flow due to it. Therefore, fish shelters are generated near the right bank of it. As a result of vertical velocity distribution which indicates the range of fish activity, maximum value are 0.0043 m/s in 30-year of return period of flood 0.0052 m/s in 50 year flood, 0.0046 m/s in 80-year of return period of flood, and 0.0039 m/s in 100-year of return period of flood. As the discharge increases, the areas of fish shelters decreases because depth and turbulent energy increase according to increases discharge. The estimated areas of fish shelters near the right bank decrease from 61.5% in 30-year of return period of flood to 39.0% 100-year of return period of flood. Therefore, the constructed hydraulic structures affect fish shelters.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.48-57
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• 2009

A two-dimensional (2D), laterally-averaged hydrodynamic and water quality model, CE-QUAL-W2 was applied to evaluate the performance on simulating the effect of flushing from Daecheong Reservoir on the downstream water quality variations during the flushing events held on November, 2003 and March, 2008. The hydraulic and water quality simulation results were compared with field measurement data, as well as a one-dimensional (1D), unsteady model (KORIV1) that revealed limited capability in the previous study due to missing the resuspension process of river bottom sediments. The results showed that although the 2D model made satisfactory performance in reproducing the temporal variations of dissolved matters including phosphate, ammonia and nitrate, it revealed poor performance in simulating the increase of biological oxygen demand and suspended sediment (SS) concentrations during the passage of the flushing flow. The reason of the error was that the resuspension process of the 2D model is only the function of shear stress induced by wind. In reality, however, as shown by significant correlation between bottom shear stress ($\tau$) and observed SS concentration, the resuspension process can be significantly influenced by current velocity in the riverine system, especially during flushing event. The results indicate that the resuspension of river bottom materials should be incorporated into the water quality modeling processes if $\tau$ is greater than a critical shear stress (${\tau}_c$) for better simulation of flushing effect.

• International Journal of Fluid Machinery and Systems
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• v.8 no.3
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• pp.142-154
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• 2015

Nowadays, computational fluid dynamics is commonly used by design engineers to evaluate and compare losses in hydraulic components as it is less expensive and less time consuming than model tests. For that purpose, an automatic tool for casing and distributor analysis will be presented in this paper. An in-house mesh generator and a Reynolds Averaged Navier-Stokes equation solver using the standard $k-{\omega}$ shear stress transport (SST) turbulence model will be used to perform all computations. Two solvers based on the C++ OpenFOAM library will be used and compared to a commercial solver. The performance of the new fully coupled block solver developed by the University of Lucerne and Andritz will be compared to the standard 1.6ext segregated simpleFoam solver and to a commercial solver. In this study, relative comparisons of different geometries of casing and distributor will be performed. The present study is thus aimed at validating the block solver and the tool chain and providing design engineers with a faster and more reliable analysis tool that can be integrated into their design process.

• Nuclear Engineering and Technology
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• v.55 no.9
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• pp.3213-3228
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• 2023

As an important part of the digital reactor, the pin-by-pin wise fine coupling calculation is a research hotspot in the field of nuclear engineering in recent years. It provides more precise and realistic simulation results for reactor design, operation and safety evaluation. CORCA-K a nodal code is redeveloped as a robust pin-by-pin wise neutronics and thermal-hydraulic coupled calculation code for pressurized water reactor (PWR) core. The nodal green's function method (NGFM) is used to solve the three-dimensional space-time neutron dynamics equation, and the single-phase single channel model and one-dimensional heat conduction model are used to solve the fluid field and fuel temperature field. The mesh scale of reactor core simulation is raised from the nodal-wise to the pin-wise. It is verified by two benchmarks: NEACRP 3D PWR and PWR MOX/UO₂. The results show that: 1) the pin-by-pin wise coupling calculation system has good accuracy and can accurately simulate the key parameters in steady-state and transient coupling conditions, which is in good agreement with the reference results; 2) Compared with the nodal-wise coupling calculation, the pin-by-pin wise coupling calculation improves the fuel peak temperature, the range of power distribution is expanded, and the lower limit is reduced more.